This invention relates to a method of and an apparatus for making a composite laminated structure comprised particularly of a sheet of polyurethane foam or other material which is similarly low in density and a polypropylene substrate or the like.
Thermoplastic plastics, particularly polypropylene, portray a variety of favorable characteristics and properties including that of being easily molded and that of chemical inertness; and thus, such plastics are ideal for a plurality of applications. Such plastics are also comparitively inexpensive, and therefore particularly desirable for use in the manufacturing of articles of commerce adapted as disposable packages for food and health and beauty aids. However, in certain packaging applications, for instance where chemical compositions are involved, the item or composition being packaged will not readily adhere to the plastic, as might be required, because of the properties of the plastic and/or the composition itself. An example of such a packaging application is where a polypropylene material is used to form a dispensing container for a solid anti-perspirant/deodorant composition.
It is these packaging applications which require some means to ensure that all compositions adhere to the polypropylene in the desired areas. The inventor herein has discovered that fixing a layer of polyurethane foam to the polypropylene is the most inexpensive and perhaps only means of accomplishing the above. When this concept is reduced to practice, all such solid compositions will readily adhere to the layer of polyurethane foam, and therefore will become fixed in relation to the polypropylene. Without such a structure, the use of polypropylene materials in the above mentioned packaging applications might not be possible or feasible from the viewpoint of cost and benefit derived therefrom.
The problem arises, however, as to the proper mechanical technique to effect the bonding of the polyurethane foam to the polypropylene. Techniques for laminating plastic resin materials are well known in the art, and include methods and apparatus by which the plastic resin material, in its entirety, is heated and the covering material is subsequently rolled or compressed on the plastic resin material in its softened state.
Thus, U.S. Pat. No. 3,533,866 discloses a method which uses a flame laminator to heat and tackify polyolefin fiber batts which are immediately laminated to a layer of flexible polyurethane foam. Similarly, U.S. Pat. No. 3,318,744 discloses a method which utilizes elongated ribbon type flames issued from a plurality of orifices to heat the surface of a polyurethane foam material which is held under tension (so as not to wrinkle). A reenforcement layer is then laminated to the polyurethane foam with a reenforcement layer. The apparatus and method disclosed in these Patents, however, are dangerous, costly, require strict supervision. Moreover, such apparatus and methods are ineffective where the polyurethane foam is of particularly low density or of relatively thin gauge.
U.S. Pat. Nos. 3,062,698 and 4,225,376 teach methods by which a covering material is heated to a temperature above the melting point of a foam thermoplastic resin, on which the covering material is immediately pressed. The methods disclosed in these patents are ineffective because they heat and soften the entire material on which the foam is to be pressed, thus deforming the shape and critical dimensions of the material.
U.S. Pat. No. 4,356,012 teaches a method which uses a heated die with a central relief groove to seal a hydrophobic filter material to a urinary bag made of polyvinyl chloride. This method is inapplicable for bonding a sheet of polyurethane foam to a polypropylene substrate because it calls for the direct sealing of two materials together, the first of which is a filter screen made of a material which is resistant to heat.
Although not shown specifically in the prior art, it should be noted that the use of a glue or an epoxy to effect the desired bonding between the foam and polypropylene substrate has been unsuccessful for two reasons. First, the types of glues and epoxies which will adhere to polypropylene plastics are limited. Secondly, the surface area of the foam susceptible to such bonding is minimal and therefore any bond which might be made is correspondingly weak. Further, gluing or epoxying smaller items can be tedious and expensive from the standpoint of manufacturing, requiring long periods of time for drying and completing the bond.
The present invention is directed to an apparatus for and a method of bonding particularly low density or thin gauge materials to substrates made of polypropylene or the like to form a composite laminated structure in which the structure, characteristics and properties of the polyurethane foam and the polypropylene substrate are not substantially altered thereby.
The broad method of bonding thin layers of low density materials to a polypropylene substrate in accordance with the present invention can be varied and altered for adaptation to a variety of manufacturing applications. By employing the apparatus and method herein, any material which has heretofore resisted bonding to polypropylene or the like, or requires expensive techniques to effect such bonding, can be readily and inexpensively bonded thereto.
The composite laminated structure obtained by the method and apparatus of the present invention can be used in the construction of many products, and in particular, to products requiring polyurethane foam as a protective cushion or to anchor a composition to a relatively strong polypropylene casing or container which can be adapted, prior to bonding the polyurethane foam thereto, for snap-fit assembly or any other means of fastening.